The invention relates to a method for providing a coating on a polyalkylene substrate. Polyalkylene, especially polypropylene, is a widely used plastic material because of its mechanical strength, high-impact resistance, rigidity and chemical resistance. A disadvantage is that coatings, such as decorative or label printings on polypropylene show a bad adherence without special measures, compared to polymers like ABS or polycarbonate. Known methods which are used to increase the adhesion of coatings on polypropylene are corona, plasma, UV/ozone, flame and chemical treatments. All these processes have certain disadvantages. A corona treatment cannot be used for curved surfaces. A plasma treatment requires expensive vacuum equipment. An UV/ozone treatment is a slow process, and a flame and chemical treatment could be dangerous in an industrial environment.
An example of a method which does not have the above disadvantages is disclosed in the abstract of JP-A-03-128947. In the known method, the polymeric substrate is irradiated with deep UV light in an oxidizing atmosphere, directly after a deep UV exposure in an inert atmosphere. A disadvantage of the known method is that the second exposure takes a relatively long time in order to obtain a good adhesion between a coating and a polyalkylene substrate surface.